Galvanic oxygen sensors are generally known. Such devices are typically constructed with a lead anode because of its reliability, stability and ease of manufacture.
However, lead is a known toxic material that should be eliminated from electronic packaging, chemical sensing and other commercial applications, due to its demonstrated deleterious effect on people's health. In recent years, there has been intensive research directed to developing lead-free oxygen galvanic sensors, as a drop-in replacement for existing portable gas detection instruments.
In general, low power/no power consumption oxygen sensors are the most attractive technical solution for portable applications because they offer the maximum operating time between re-charging periods. The major advantage of oxygen galvanic sensors for portable instruments is the fact that they are self-powered, and they have a simple signal conditioning circuit for sensor read-out, consisting of a load resistor connected between the consumable anode and the cathode and/or a current follower circuit.
Recently developments have proposed the use of different base metals like zinc, aluminum and tin (EP 1 593 962 A1, and EP 2 219 024 A1) as a possible replacement for the lead anode in electrochemical galvanic oxygen sensors with consumable anodes. However, it is difficult to control the rate of consumption of the anode using such metals working in a capillary limited mode.
In general, a projected lifetime of at least two years is necessary for possible substitutes for lead anodes in electrochemical galvanic oxygen sensors. However, it does not appear that such lifetimes can be achieved using metals such as zinc, aluminum or tin. Accordingly, a need exists for other alternatives in the construction of electrochemical galvanic oxygen sensors.